Characterization of an enterotoxigenic Escherichia coli strain from Africaexpressing a putative colonization factor

An enterotoxigenic Escherichia coli (ETEC) strain of serotype O114:H- that expressed both heat-labile and heat-stable enterotoxins and tested negative for colonization factors (CF) was isolated from a child with diarrhea in E gypt. This strain, WS0115A, induced hemagglutination of bovine erythrocytes and adhered to the enterocyte-like cell line Caco-2, suggesting that it ma y elaborate novel fimbriae. Surface-expressed antigen purified by different ial ammonium sulfate precipitation and column chromatography yielded a sing le protein band with M-r 14,800 when resolved by sodium dodecyl sulfate-pol yacrylamide gel electrophoresis (16% polyacrylamide). A monoclonal antibody against this putative fimbrial antigen was generated and reacted with stra in WS0115A and also with CS1-, CS17-, and CS19-positive strains in a dot bl ot assay. Reactivity was temperature dependent, with cells displaying react ivity when grown at 37 degrees C but not when grown at 22 degrees C. Immuno blot analysis of a fimbrial preparation from strain WS0115A showed that the monoclonal antibody reacted with a single protein band. Electron microscop y and immunoelectron microscopy revealed fimbria-like structures on the sur face of strain WS0115A. These structures were rigid and measured 6.8 to 7.4 nm in diameter. Electrospray mass-spectrometric analysis showed that the m ass of the purified fimbria was 14,965 Da. The N-terminal sequence of the f imbria established that it was a member of the CFA/I family, with sequence identity to the amino terminus of CS19, a new CF recently identified in Ind ia. Cumulatively, our results suggest that this fimbria is CS19. Screening of a collection of ETEC strains isolated from children with diarrhea in Egy pt found that 4.2% of strains originally reported as CF negative were posit ive for this CF, suggesting that it is biologically relevant in the pathoge nesis of ETEC.